Answer this question truthfully
### Question: What are the causes of Astigmatism?
### Response: The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness. A minor degree of astigmatism is considered normal and does not require correction. Astigmatism is very common.
Astigmatism may sometimes develop due after eye surgery or following an eye injury . Additionally, severe astigmatism may result from a somewhat rare condition called keratoconus , which is a degenerative non-inflammatory disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve.